Channel Mobility Boosting in a Poly-Si Channel Using Ge Diffusion Engineering and Hydrogen Plasma Treatment

We demonstrated that channel mobility and cell current could be increased through Ge diffusion engineering and H-2 plasma treatment in a poly-Si channel. Even though the Ge channel has a higher intrinsic mobility than the Si channel, a typical poly-SiGe channel has inferior channel characteristics due to high interface trap density (D-it) and bulk trap density caused by Ge. We propose a novel technique to control the Ge profile along the depth direction of the channel to realize lower Ge concentration at the gate dielectric interface and higher Ge concentration at the channel bulk. This Ge profile could achieve reduced D-it and enhanced channel mobility. Furthermore, the bulk traps caused by Ge are effectively reduced by H-2 plasma treatment. These techniques increased the channel mobility to 32%, which can help increase the channel mobility of devices where poly-Si channels are used.